No other pathogen causes more mortality than Mycobacterium tuberculosis with nearly 2 million deaths per year. Through an ability to characterize membrane protein structure in various membrane mimetic environments, functional knowledge of potential drug targets can be greatly advanced. Membrane proteins represent the majority of these targets, yet only one out of 1200 putative membrane proteins in the Mtb genome is characterized and only a few others are well modeled by homology with proteins from closely related species. We propose here to characterize the backbone structure and dynamics and to gain mechanistic knowledge of the biological function of four significant membrane proteins from the Mtb genome. Understanding membrane protein structure and function represents a major scientific frontier that is profoundly important to the Nation's and the World's health. For M. tuberculosis there have been no new drugs in the past few decades although there are quite a few potential drugs in the pipeline. Extensively drug resistant Mtb, which killed 52 of 53 patients in South Africa last year is now thought to have spread to many poor and undeveloped countries on the African continent. Furthermore, the lengthy drug regimen necessitated by the latent state of Mtb greatly complicates treatment. Therefore, understanding entry and exit from the latent state is very important. Many obstacles have conspired to impede the structural characterization of membrane proteins (0.3% of the structures in the Protein Data Bank versus 30% of most genomes). As with all of the structural methods the primary challenge has been in sample preparation. Over the past year very significant progress has been made in this arena for solution and solid-state NMR. Not only is sample preparation challenging, but membrane proteins have multiple conformational and functional states complicating the functional understanding of these proteins and necessitating more structural work. In addition, their dynamics is more complex reflecting a heterogeneous environment;and they form complexes with a different balance of molecular interactions. These four proteins include CorA for which there is already a crystal structure from Thermatoga maritima for the closed state of this Mg2+ transporter. We propose to characterize the Mtb transmembrane domain and develop a model for Mg2+ transport by CorA. For the Kdp complex we will focus on the essential KdpC protein that is thought to have a coordinating role in this K+ transport system. ChiZ is thought to be an inhibitor of cell division and potentially a regulator of entry into the latent state. Rv1861 appears to be a octameric protein that hydrolyzes ATP and potentially forms a complex with a glycosyltransferase.
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